DESCRIPTION (Applicant's Description): Researchers are increasingly using new methods for controlling gene expression in whole animals to investigate the regulation of normal mammary gland development and neoplasia. The purpose of this meeting is to conduct the first comprehensive discussion about the use of new molecular genetic mouse models for understanding the mechanisms operative in mammary gland morphogenesis, differentiation, involution, and neoplasia. Opportunities for gaining insight into mechanisms of human beast cancer from these models will be a central focus. The specific objectives are to (1) communicate recent advances in understanding the molecular and cellular mechanisms controlling normal mammary development; (2) delineate current hypotheses regarding oncogenesis in the mammary gland, including molecular pathways, modes of activation, and processes of cellular transformation and disease progression; (3) define the utility of the mouse for modeling human breast disease through discussion on mouse strains carrying targeted mutations in human susceptibility genes and comparative pathobiology; (4) explain emerging technologies for targeting gene expression to the mammary gland at specific times; (5) discuss the resources available to the community and determine whether additional resources are needed; (6) define promising areas for new research through discussions on the pressing questions about molecular mechanisms in human breast cancer that can be answered using mouse models; and (7) compile a Proceedings to be published on the World Wide Web that will serve as a timely resource for investigators interested in learning about the mouse as a model for breast cancer research.